cell communication Flashcards
how many cells are multicellular organisms made out of?
trillions of cells
how do cells coordinate activitues?
they “talk” to each other/ communicate
what kingdom in yeast from?
fungi
is yeast motile?
it is nonmotile
yeast is used to make what?
beer, bread, wine
name of yeast cell we study
Saccharomyces cerevisiae
what are the two sexes of mating types for yeast cell called?
a and alpha cell
how do two haploid yeast cells mate?
the a cell secretes a signaling molecule/pheromone (a factor) which binds to receptors on a nearby alpha cell
at the same time, the alpha cell secretes the alpha factor which binds to a receptor on the a cell
what does the attachment of a cell’s factor to another cell’s receptor do?
causes the cells to start shmooing
what is shmooing?
cells to elongate and grow toward each other
what happens when the two haploid cells meet each other?
they form a new diploid a/alpha cell
what is the more typical way for yeast cells to repoduce?
asexually by pinching off a parent cell - budding
bacteria can live as free-living cells called?
planktonic bacteria
how do bacteria cells communicate?
with small molecules that can be detected by other bacterial cells of the same species
what happens when the signaling molecules of bacteria cells gets high?
induces quorum sensing
what is quorum sensing?
bacteria are indicated that their densities are high enough to coordinate behaviors that can only be done by a given number of bacterial cells working together in synchrony
who discovered quorum sensing?
Bonnie Bassler
example of quorum sensing
formation of biofilm
what is biofilm ?
aggregation of bacterial cells adhered to a surface
slimy feeling on teeth each morning or on leaves in a forest path
what do cells get from the surfaces they are attached to?
typically derive nutrients
where was quorum sensing fist seen by Bassler?
in a species of bioluminescent bacteria called Vibrio fischeri that are mutualistic symbionts in the light producing organs of squid
how does Vibrio fischeri work?
as free-living planktonic cells, their signaling molecules are too low to produce light. however, in high concentrations, this triggers protein synthesis of luciferase that produces the characteristic glow
what does pathogenic mean?
disease causing
example of pathogenic bacteria using quorum sensing
rely on this to know when their densities are high enough to turn on their genes for virulence
what is virulence?
harmful characteristic
what is local signaling?
when eukaryotic cells communicate through direct contact
includes plant and animal cell functions and cell-cell recognition when surface molecules interact
local signaling in animal cells?
gap junction
local signaling in plant cells?
plasmodesmata
example of cell to cell recognition
glycoprotein to protein receptor
2 steps involved in Salmonella becoming virulent
- activate gene
- release toxins
what does local signaling also involve regarding communication by travelling short distances?
involves messenger molecules being secreted from one cell from traveling short distances toa target cell which then carried out a response
what are local regulators?
messenger molecules
growth factor stimulate nearby target cells to grow and divide
what is paracrine signaling?
when the secreting cell releases a lot of local regulators, to the point where they affect many target cells in the vicinity
specialized type of local signalinh
synaptic signaling - occurs in animal neurons or muscle cells where the messenger molecules are neurotransmitters
synonymous names for messenger molecules
ligand, signaling molecules, local regulators
what do plants and animals use for long-distance signaling?
chemicals called hormones
long distance signaling in animals
endocrine signaling - begins when secreting cells release hormone that travel via the bloodstream to remotely located target cells that then carry out a cellular response
via nervous system with the aid of neurons - longest nerve is sciatic nerve
what determine the ability of a target cell to respond to a signaling molecule?
whether it had a protein receptor that can bind with the signaling molecule
what happens once the signaling molecule binds to a receptor?
transduction - transduces (changes) the molecule into another form
once changed the target cell can now respond
what three steps does cell communication involve?
reception
transduction
response
what is reception?
signaling molecule binds to a receptor protein either on the cell’s surface or inside the cell
what is transduction?
the signaling molecule changes the receptor protein in some way
signal transduction pathway
what is signal transduction pathway?
a pathway of several steps where each relay molecule brings about change to the next molecule
a series of steps linking a stimulus to a specific cellular response
what is response?
can be almost any imaginable cellular activity
ex. activating a gene in the nucleus, stem cells undergoing differentiation into specialized cells, or apoptosis
how do signaling molecules relate to radio stations?
radio stations broadcasts its signal indiscriminately, but it can only be picked up by radios on the right wavelength
in the same way, signaling molecules might be sent into the bloodstream and encounter many cells along its path, but can only be detected by a specific receptor protein on or in the target cell
signaling molecule behaves as a ligand - general term for a molecule that binds specifically to another molecule, often a larger one
what does the ligand binding cause? (2)
1) receptor protein to change its shape, activating the receptor
2) the aggregation of two of more receptors molecules, resulting in further molecule events inside the cell
what is a common cell - surface transmembrane receptor?
spans across the phospholipid bilayer of the cell membrane
G protein-coupled receptor (GPCR)
what type of 2 protein structure makes up GPCR?
7 alpha helices
GPCR are widespread. what are some roles they play?
embryonic Develpoment, vision, taste, and smell
roles in human diseases like cholera, pertussis, and botulism by producing toxins that interfere with this system
60% of all medicines today exert their effects on G protein pathways
how does GPCR work?
- GPCR is switched off. The G protein has GDP (guanosine diphosphate) attached to it and is inactive
- GPCR is turned on when a ligand binds to the extracellular side of the receptor. It is then activated and changes shape. then it binds the G protein causing GDP to be converted to GTP (guanosine triphosphate, and energy rich molecule)
- The G protein detaches from the GPCR and then binds to an enzyme, changing the enzyme’s shape. the enzyme will trigger the next step, eventually leading to a cellular response. meanwhile, the signaling molecule detaches from the GPCR/it is reversible
- the G protein hydrolyzes GTP back into GDP and is inactive once gain as it leaves the enzyme, and the enzyme returns to it og shape. the system in now ready for the nest signaling to bind to GPCR
another example of cell-surface receptor
receptor tyrosine kinase
what is tyrosine?
amino acid
what is kinase?
an enzyme that catalyzes the transfer of phosphate groups - phosphorylation
what can be activated if one ligand binds to a RTK?
10+ transduction pathways and cellular responses
what are abnormal RTKS associated with?
many kinds of cancer
patients with breast cancer cells who have excessive levels of a RTK called HER2 have poor prognosis
how have researchers increased breast cancer survival rate by more than 1/3?
developed a protein that binds to HER2 and inhibits tumor development
how does RTK work? (4)
- before ligand binds to the RTK, the receptors exist as separate units (inactive monomers)
- the ligand binds, and the receptor monomers come together to form a dimer
- each tyrosine gets phosphorylated by ATP, which activates RTK
- now activated, relay proteins inside the cell bind to a specific tyrosine, causing transduction, and leading to a cellular response
another example of cell surface receptor
ligand-gated ion channels
how do ligand-gated ion channels work? (2)
act as “gate” when a ligand binds to them in that they open or close
the ligand then allows the flow of specific ions in or out of the cell
what system do ligand-gated ion channels play an important role in?
nervous system
where are intracellular receptors found?
found either in the cytosol or nucleus of the target cell
intracellular receptors characteristic
ex
hydrophibic or small - to get through the plasma membrane and phospholipid’s nonpolar tails
ex. steroid hormones (lipids) or small gas molecules (NO)
how does testosterone work with intracellular receptors? (4)
- testosterone passes through the plasma membrane
- testosterone binds to a receptor protein in the cytoplasm, activating it (transduction)
- the hormone receptor complex enters the nucleus and binds to a specific gene
- proteins synthesis creates proteins to control male sex characteristic (cellular response)
how many steps does transduction consist of?
involves multiple steps - a single transduction pathway
what is the benefit of having multiple steps?
the ability to greatly amplify a signal and more opportunities for coordination and regulation of a cellular response
how do signal activated receptor activate another molecule?
like falling dominoes - one actives another, and yet another and so in until a protein is activated to carry out a response
what are “relay” molecules?
often proteins and at each step in the pathway, they are transduced into a different shape or form
how is the shape change brought about?
by phosphorylation
what is protein kinase?
an enzyme that transfers phosphate groups from ATP to a protein
what do you call a transduction pathway that consists of relay molecules that are a bunch of protein kinases?
phosphorylation cascade
since phosphate groups have negative charges, what types of R groups on the protein kinases would they most likely interact with?
positively charged (ionic or polar)
protein kinases regulate thousands of proteins in a cell. what can abnormal protein kinases result in?
cancer
equally important are enzymes that remove phosphate grips from the activated protein kinases making them inactive and available for reuse. what are these called?
protein phosphatase - PP
process of removing phosphate groups from activated kinase?
dephosphorylation
are all components in a signal transduction pathway proteins?
no - some are secondary messengers
examples of secondary messengers
some are water-soluble/polar molecules like cAMP or ions (Ca+2) or polyatomic ions (IP3)
what is cAMP?
cyclic AMP
what is IP3?
inositol triphosphate
what are “first messengers”?
signaling molecule that binds to receptors
what are “second” messengers?
all small nonprotein components of a signal transduction pathway
what does cAMP stand for?
cyclic adenosine monophosphate
how is cAMP made?
an enzyme called adenylyl cyclase removes 2 inorganic phosphate groups from ATP and forms a “cyclic” structure
what enzyme then converts cAMP back into ATP?
phosphodiesterase
what happens when the G protein coupled receptor binds a ligand?
GPCR chape changes
G protein binds to CPCR
what happens when the G protein binds to the GPCR?
GDP becomes GTP - now G protein is activated
what does the activated G protein do?
binds to enzyme adenylyl cyclase change its shape and converting ATP to secondary messenger cAMP
what does cAMP do after being formed?
activates a protein kinase which would then phosphorylate other proteins
how does phosphodiesterase convert cAMP to AMP?
hydrolysis
what is cholera?
a disease where H2O supply is contaminated with human feces containing the cholera bacteria
causes profuse diarrhea to infected persons, and if left untreated its victims soon die from salt and water loss
cholera bacteria
Vibrio cholera
how does V cholera infect cells?
bacteria form a biofilm on the small intestine and produce toxin
that toxin is an enzyme that changed G protein involved in salt and water secretion
G protein can no longer hydrolyze GTO back to GDP, so it stays in active form, continually stimulating adenylyl cyclase to make cAMP
this causes large amounts of salts to go into the intestines and via osmosis water soon follows
what responses does Ca+2 cause in animal cells?
muscle contractions and cell division
what responses does Ca+2 cause in plant cells?
greening in response to light
where does IP3 come from?
cleaving a phospholipid
what leads to protein synthesis?
many signaling pathways lead to turning off or on specific genes in the nucleus
what is protein synthesis comprised of?
transcription and translation
what is transcription?
DNA -> mRNA
what is translation?
mRNA -> protein
what is the common name for epinephrine?
adrenaline
epinephrine allows for what response?
the “fight” or “flight” response
what polysaccharide is being broken down in this cellular pathway to fuel the response of epinephrine?
glycogen is being broken down into a form of glucose (to provide energy in cellular respiration)
what steps does a fine-tuned response of epinephrine have? (4)
1) amplification - of signal so that 1 signal molecule can influence 10^8 molecules in the end
2) cell specificity - epinephrine breaks down glycogen in a liver/muscle cell but when it binds to a heart cell it causes it to contract/ increase heart rate
3) signaling efficiency - scaffolding proteins group together relay proteins, so the process is sped up
4) termination - needs to inactivate each molecule in the path and make sure it only lasts a short time so that the cell is ready to receive a fresh signal
how does a cell undergo apoptosis?
uses nucleases to chop up DNA and proteases to break up proteins, along with disassembling all the organelles
cell then shrinks and becomes lobed before being engulfed and digested by scavenger cells
what is the name for a change in which a cell becomes lobbed and shrunked?
blebbing
what signals apoptosis in cells as it is usually inhibited?
a death signal molecule activates apoptosis genes to encode caspases
apoptosis genes
ced-3 and ced-4
what does ced stand for?
cell death
what are caspases?
nuclease and protease enzymes
in what does apoptosis play a critical role in?
embryonic development
apoptosis role examples
morphogenesis of hands and feet
development of nervous system - babies have twice as many of neural connections than an adult
morphogenesis
“morpho” - change/look
“genesis” - creation
if it weren’t for apoptosis, what type of hands and feet would humans have?
webbed
what disease are a result of apoptosis?
some degenerative diseases
Parkinsons’ - death of neurons that make dopamine to help control muscle movement
cancer - melanoma
what are the ABCDE of melanoma?
asymmetry
border
color
diameter
evolve
